Incorporating nisin and grape seed extract in chitosan-gelatine edible coating and its effect on cold storage of fresh pork
Introduction
Pork is one of the most consumed meat products worldwide (McGlone, 2013). However, its high levels of polyunsaturated fatty acids make it susceptible to oxidation and microbial spoilage, which leads to colour changes, off-flavours, and rancidity (Huang et al., 2015). Therefore, preventing oxidation and microbial contamination has been an important task for fresh pork preservation. Numerous innovative packaging technologies have been developed in meat preservation, such as vacuum packaging, modified atmosphere packaging, intelligent packaging, active packaging and edible packaging (Fang et al., 2017, Gertzou et al., 2017, Karabagias et al., 2011, McMillin, 2017). Recently, edible packaging (edible film or coating) has attracted great attention from researchers. Compared with conventional packaging, edible films or coatings are directly applied on the surface of food to maintain food quality and extend shelf life. The main advantage is that edible coatings or films can meet consumers’ demand for convenience, food quality and safety (Embuscado & Huber, 2009). Besides, the edible packaging materials are mainly derived from natural food-grade materials, which have edible, non-toxic, bioactive and biodegradable properties simultaneously, that may not found in synthetic packaging materials (Hassan, Chatha, Hussain, Zia, & Akhtar, 2018).
Various natural materials have been used to develop edible packaging, mainly polysaccharides (e.g. alginate, pectin and chitosan), proteins (e.g. whey, collagen, gelatine) and lipids (e.g. wax) (Hassan et al., 2018). Among them, chitosan has been extensively studied and applied in the food industry owing to the unique film-forming properties, low gas permeability, antioxidant activity against lipid oxidation, and more importantly, antimicrobial activity against bacteria and fungi (Elsabee and Abdou, 2013, No et al., 2007). However, the disadvantage is that it has a relatively high moisture permeability (Elsabee & Abdou, 2013). Gelatine, derived from the degradation of bone or skin collagen of piscine or bovine, is another coating material which has been extensively researched (Gomez-Guillen et al., 2009). It has been reported that chitosan and gelatine together can form a compact structure by hydrogen bonding, which can effectively enhance the moisture permeability while improving the softness and flexibility of the film/coating (Pereda, Ponce, Marcovich, Ruseckaite, & Martucci, 2011). Several studies have shown that chitosan-gelatine film/coating can effectively improve the preservation of meat products. For example, Cardoso et al. (2016) found that a film composed of 0.5–1.0% chitosan and 3–6% gelatine preserved the colour and significantly inhibited the lipid oxidation of beef steaks in retail display. Farajzadeh, Motamedzadegan, Shahidi, and Hamzeh (2016) also observed that 1% chitosan-3% gelatine coating could extend the shelf-life of shrimps from 7 days to 13 days during cold storage.
In addition, incorporation of natural bioactive compounds such as gallic acid (Fang, Lin, Warner, & Ha, 2018), nisin (Cao, Warner, & Fang, 2019) and grape seed extract (Sivarooban, Hettiarachchy, & Johnson, 2008) has been an effective way to further enhance the preservation performance of the edible coating/film. Nisin is a bacteriocin produced by Lactococcus lactis and has been widely used in the food industry due to its ability to inhibit various of Gram-positive bacteria such as lactic acid bacteria, which is a major cause of meat spoilage during cold storage (Punyauppa-path, Phumkhachorn, & Rattanachaikunsopon, 2015). Grape seed extract is another natural material and is well known for its high levels of phenolic contents such as phenolic acids, flavonoids and tannins, which possesses potent antimicrobial and antioxidant activities, and has a potential to be utilised as a functional food ingredient to improve food safety and quality (Nowshehri, Bhat, & Shah, 2015).
However, to our knowledge, no research has investigated the chitosan-gelatine edible coating incorporating grape seed extract and/or nisin on fresh meat preservation. Therefore, the objective of this study was to develop an edible coating system by incorporating grape seed extract and/or nisin into the chitosan-gelatine solution, and investigate its effect on the fresh pork quality during cold storage, which has the potential to be developed as a practical commercial method for fresh meat preservation.
Section snippets
Materials
Chitosan (degree of deacetylation > 90.0%), gelatine powder, and grape seed extract (proanthocyanidins > 95%) were purchased from Solarbio Science & Technology Co., Ltd. (Beijing, China), Sciyu Biotech, Co. Ltd. (Xi'an, China) and Thermo Fisher Scientific (Scoresby, VIC, Australia) respectively. Plate count agar was obtained from Becton & Dickinson (North Ryde, NSW, Australia). Nisin (from Lactococcus lactis, 106 IU/g in 2.5% balance sodium chloride) and other chemicals used in the study were
pH value
pH value is an important indicator of fresh meat quality. The pH of fresh pork normally ranges from 5.10 to 6.36, and a pH range of 5.7–6.1 is more likely to be favoured by consumers (Kim et al., 2016, Wright et al., 2005). The initial pH value (at day 0) of fresh pork was 5.80, and the value gradually decreased during the first 15 days of cold storage. However, no significant difference was observed among all samples for the first 10 days (Fig. 1). The slow decline of the pH values may be due
Conclusion
The present study developed several chitosan and gelatine based edible coatings for fresh pork preservation. Chitosan coating (CHI) alone effectively extended the shelf-life of pork by minimising the pH change, preventing lipid and protein oxidation and inhibiting microbial growth during the 20 days of cold storage at 4 °C. These preservative effects were enhanced by combining chitosan with gelatine (CHI-GEL), possibly owing to the compact structure formed between chitosan and gelatine.
Declaration of competing interest
The authors declare no conflict of interest.
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